A major challenge in the area of the parenteral administration of biologically active materials is the development of a controlled delivery device that is small enough for intravenous application and which has a long circulating half-life. Biologically active materials administered in such a controlled fashion into tissue or blood are expected to exhibit decreased toxic side effects compared to when the materials are injected in the form of a solution, and may reduce degradation of sensitive compounds in the plasma.
A number of injectable drug delivery systems have been investigated, including microcapsules, microparticles, liposomes and emulsions. A significant obstacle to the use of these injectable drug delivery materials is the rapid clearance of the materials from the blood stream by the macrophages of the reticuloendothelial system (RES). For example, polystyrene particles as small as sixty nanometers in diameter are cleared from the blood within two to three minutes. By coating these particles with block copolymers based on poly(ethylene glycol) and poly(propylene glycol), their half-lives were significantly increased. L. Illum, S. S. Davis, "The organ uptake of intravenously administered colloidal particles can be altered by using a non-ionic surfactant (poloxamer 338)", FEBS Lett., 167, 79 (1984). Polystyrene particles, however, are not biodegradable and therefore not therapeutically useful.
Liposomal drug delivery systems have been extensively considered for the intravenous administration of biologically active materials, because they were expected to freely circulate in the blood. It was found, however, that liposomes are quickly cleared from the blood by uptake through the reticuloendothelial system. The coating of liposomes with poly(ethylene glycol) increases their half life substantially. The flexible and relatively hydrophilic PEG chains apparently induce a stearic effect at the surface of the liposome that reduces protein adsorption and thus RES uptake. T. M. Allen, C. Hansen, Biochimica et Biophysica Acta, 1068, 133-141 (1991); T. M. Allen, et al., Biochimica et Biophysica Acta, 1066, 29-36 (1991); V. Torchilin, A. Klibanov, "The antibody-linked Chelating Polymers for Nuclear Therapy and Diagnostics", Critical Reviews in Therapeutic Drug Carrier Systems, 7(4), 275-307 (1991); K. Maruyama, et al., Chem. Pharm. Bull., 39(6), 1620-1622 (1991); M. C. Woodle, et al., Biochimica et Biophysica Acta; 193-200 (1992); and D. D. Lassic, et al., Biochimica et Biophysica Acta, 1070, 187-192 (1991); and A. Klibanov, et al., Biochimica et Biophysica Acta, 1062, 142-148 (1991).
European Patent Application Nos. 0 520 888 A1 and 0 520 889 A1 disclose nanoparticles of the block copolymer of polylactic acid and poly(ethylene glycol) for the injectable controlled administration of biologically active materials. The applications do not disclose how to modify the copolymer to vary the profile of drug release nor how modification of the copolymer would affect distribution and clearance of the delivery devices in vivo. The applications also do not teach how to prepare nanoparticles that are targeted to specific cells or organs, or how to prepare nanospheres that are useful for gamma-imaging for diagnostic purposes.
U.S. Pat. No. 5,145,684 discloses stable, dispersible drug nanoparticles prepared by wet milling in the presence of grinding media in conjunction with a surface modifier.
It would be desirable to have injectable particles for the controlled delivery of biologically active materials that are not rapidly cleared from the blood stream by the macrophages of the reticuloendothelial system, and that can be modified as necessary to target specific cells or organs or manipulate the rate of delivery of the material.
Therefore, it is an object of the present invention to provide injectable particles for the controlled delivery of biologically active materials that are not rapidly cleared from the blood stream.
It is another object of the present invention to provide injectable particles that can be modified as necessary to target specific cells or organs or manipulate the rate of delivery of the material.
It is another object of the present invention to provide injectable biodegradable particles that contain magnetic materials for diagnostic imaging.
It is still another object of the present invention to provide microparticles for the controlled release of substances or for diagnostic imaging that can optionally be targeted to specific organs or cells.